Carbon-Based Nanostructures as Advanced Contrast Agents forMagnetic Resonance Imaging

摘要

Superparamagnetic carbon-based nanostructures are presented as contrast agents(CAs) for advanced imaging applications such as cellular and molecular imaging usingmagnetic resonance imaging (MRI). Gadolinium-loaded, ultra-short single-walled carbonnanotubes (gadonanotubes; GNTs) are shown to have extremely high rl relaxivities(contrast enhancement efficacy), especially at low-magnetic field strengths. The inherentlipophilicity of GNTs provides them the ability to image cells at low magnetic fieldstrength.A carboxylated dextran-coated GNT (GadoDex) has been synthesized andproposed as a new biocompatible high-performance MRI CA. The rl relaxivity is ca. 20times greater than for other paramagnetic Gd-based CAs. This enhanced relaxivity forGadoDex is due to the synergistic effects of an increased molecular tumbling time ('tR)and a faster proton exchange rate ('tm).GNTs also exhibit very large transverse relaxivities (r2) at high magnetic fields ~3 T). The dependence of the transverse relaxation rates (especially R2 *) of labeled cellson GNT concentration offers the possibility to quantify cell population in vivo using R2 *mapping. The cell-labeling efficiency and high transverse relaxivities of GNTs hasenabled the first non-iron oxide-based single-cell imaging using MRI.